The present invention is directed generally to ventricular catheters which have been previously implanted in-vivo into one or more ventricles of the human brain for therapeutic purposes; and is particularly directed to removing adherent tissue occlusions of ventriculoperitoneal shunts employed in pediatric neurosurgical techniques for release and fluid flow of cerebral-spinal fluids
The present invention is usefully employed with ventricular catheters which have been therapeutically implanted in-vivo into the human brain; but which have become blocked by the surrounding cranial tissue which has occluded the intake drainage holes within the implanted catheter and become adherent to the catheter itself. In order to properly appreciate both the medical problem and the improved bipolar coagulator device which is employed therapeutically to alleviate such occlusion conditions in-situ, an in-depth description of the relevant medical and therapeutic use circumstances is provided below.
The four ventricles of the human brain are interconnected cavities that produce and circulate cerebral-spinal fluid (CSF). Procedures involving ventriculostomy (i.e., placement of a catheter into the ventricular system of the brain) form a major part of a neurosurgeon""s clinical practice. General areas for application of ventricular catheter placement include intracranial pressure monitoring (ICP), draining or shunting of CSF and the installation of pharmacological therapeutic agents.
CSF drainage is a major life-sustaining therapy for patients with congenital or acquired hydrocephalus. CSF drainage, which can only be performed with an intraventricular catheter, is a life-preserving procedure, because it can immediately reduce intracranial pressure. The ventricular catheter, used to drain cerebral-spinal fluid, is connected to a peripheral subcutaneous drainage system, i.e., to the peritoneal cavity or systemic circulation via the heart. However, later catheter obstruction by tissue and debris is a common, sometimes life-threatening problem.
Standard procedures for ventricular catheterization are disclosed in the textbook literature. See, for example, Neurosurgery, edited by Robert H. Wilkins and Setti S. Rangacharty, Section A, Chapter 13, Techniques of Ventricular Puncture (McGraw Hill 1984).
A frequently chosen site for ventricular catheterization is the coronal plane. In most cases, a catheter is inserted in the anterior horn of the lateral ventricle through an orifice or burr hole drilled just anterior to the coronal suture in the midpupillary line of the cranium, i.e., in the frontal bone over the ventricle. This is known in the field as Kocher""s point. The burr hole, only slightly larger than the diameter of the selected catheter to insure a snug fit and provide a seal against CSF leakage, is placed approximately 1 cm, anterior to the coronal suture, approximately 10 to 12 cm. above the nasion, and approximately 2 to 3 cm. from the midline over the nondominant hemisphere. After the burr hole is made, the dura and underlying pia-arachnoid are opened and coagulated, for example, with a fine-tipped blade after cauterizing the dural surface.
A pre-measured catheter having a stylet is then introduced and directed freehand through the burr hole, approximately in the coronal plane, and angled towards the medial canthus of the ipsilateral eye, using external landmarks such as the inner canthus of the eye in the frontal plane and a point just in front of the external auditory meatus in the lateral plane as guides to placement. CSF should flow freely from the catheter tip at a depth of approximately 4 to 5 cm. from the interior cranial surface.
A distinctive xe2x80x9cgivexe2x80x9d, or release of opposition, can often be felt when the ventricle is penetrated. Pressure should be measured at this point, since an artificially low value will be obtained even if small amounts of fluid are lost. Then, after removal of the stylet from the catheter, advancement another 1 cm. or so should insure placement in the frontal horn at a depth of about 5 to 6 cm. from the external table of the skull, care being taken that CSF continues to flow.
A variety of ventricular catheters and a range of methods for guiding a catheter into the ventricular system of the human brain are conventionally known and used. Merely illustrating this range and variety are: U.S. Pat. Nos. 5,569,267; 5,030,223; 4,860,331; 4,613,324; 4,392,307; 4,386,602; 3,934,590; 3,223,087; 3,073,310; 3,053,256; 3,817,887; and the references cited within each of these printed publications.
Ventriculoperitoneal (VP) shunt placement for hydrocephalus is one of the most common procedures in neurological surgery. Hydrocephalus may result from subarachnoid hemorrhage, trauma, tumors, and the like. The technique entails introducing a catheter through brain tissue into one of the lateral ventricles of the brain. Cerebrospinal fluid in the ventricle may be vented through the catheter to relieve signs, symptoms, and sequelae of hydrocephalus.
The current surgical technique for placement of VP shunts was developed in the 1950s by Scarff and has persisted with few modifications. Despite the relative simplicity of this procedure, the complication rate can be significant and includes operative morbidity as well as post-operative infections and tissue obstructions.
Surgical technique plays a major role in reducing complications associated with VP shunts. Improper placement of the ventricular catheter may result in neurologic injury from the misplaced catheter or may cause an early proximal shunt obstruction, which is often secondary to blockage by adherent choroid plexus and other debris. The incidence of misplaced catheters is variable and dependent on a variety of factors, including the experience of the surgeon, the size of the targeted ventricle, the surgical approach, and the use of intraoperative guidance, such as fluoroscopy, ultrasound, or endoscopy. Thus, to optimize shunt function and minimize morbidity proper placement of the proximal catheter is essential.
Two surgical approaches have been principally used for VP shunt placement, frontal and parieto-occipital. To assist in placement into small ventricles, a frontal catheter guide has been developed by Ghajar for placement of frontal ventricular catheters [Ghajar J B, J. Neurosurg. 68: 318-319 (1988)]. This instrument capitalized on the anatomical observation that a line passing perpendicular to the skull at the coronal suture will intersect the lateral ventricle.
However, parieto-occipital catheter placement has some advantages over frontal catheter placement. The catheter path necessary for the frontal approach to the ventricles traverses frontal lobe regions having a low seizure threshold. Mechanical irritation of the neural tissue surrounding the catheter may give rise to epileptogenic foci independent of the underlying cause of hydrocephalus. This complicates patient management and increases health care cost, as well as markedly impacting the patient""s quality of life.
The anatomy of the head and neck also cause technical difficulties for the surgeon. The distal end of the shunt is subcutaneously tunneled to the peritoneal cavity for implantation. Implantation in the open peritoneum provides an outlet for excess fluid drainage from the ventricles. The catheter path to the abdomen is circuitous from the frontal burr hole, however. The tube must pass posterior to the ear, and generally requires an additional skin incision. These difficulties frequently cause major complications and tissue obstructions.
Although generally successful and widely accepted by both neurosurgeons and patients, the ventriculoperitoneal shunt (xe2x80x9cVPSxe2x80x9d) and indeed all shunting systems, regularly malfunction despite the best efforts of physicians and biomedical engineers. These malfunctionsxe2x80x94once commonly the result of material, construction, or mechanical failuresxe2x80x94now relate primarily to necessary compromises or technical errors occurring during shunt placement or revision that occur coincident to successful cerebrospinal fluid diversion. VPS malfunction rates are maximal during the first year after insertion (see Ventureya et al., Neurosurgery 34: 924-926 (1994)].
Malfunction is most commonly caused by obstruction of the ventricular catheter by choroid plexus, ventricular ependyma, or xe2x80x9cdebrisxe2x80x9d. Ventricular catheter obstruction typically occurs in 80 to 90% of VPS malfunctions; and has become the predominant cause of obstruction because rigorous techniques have reduced the incidence of other causes of malfunction. Moreover, such ventricular catheter obstructions remain a major unsolved problem despite current improvements in materials or in catheter design changes, such as the Portnoy catheter [Haase et al., Acta Neurochir (Wien) 33: 213-218 (1976)]; and despite increased emphasis on precise techniques favoring optimal catheter placement [see for example: Ehni, G., Neurosurgery 14: 99-110 (1984); Epstein, F., Clin. Neurosurg. 32: 608-631 (1985); Gutierrez-Lara et al., J. Neurosurg. 42: 104-107 (1975); Nolsen, F. E. and D. P. Becker, Clin. Neurosurg. 14: 256-273 (1966) and J. Neurosurg. 20: 362-374 (1967)].
A ventricular tube, a catheter, having many sidewall holes in its head part and used for the above described purposes is well known, but these sidewall holes are often blocked by choroid plexus tissues which penetrate into the ventricular tube through the holes. In order to prevent this blockage, various device improvements have been proposed. These include the following illustrative examples: A drainage tube made of silicone [U.S. Pat. No. 4,182,343]; an external cerebrospinal fluid drain apparatus [U.S. Pat. No. 5,683,357]; a drain cannula [U.S. Pat. No. 5,913,852]; and improved devices and methods for parieto-occipital placement of ventricular catheters [U.S. Pat. Nos. 5,569,267; 6,197,003; and 5,683,357].
In addition, a number of other innovations have been put forward as alternative preventative improvements. These are represented by an electrolyte fluid flow rate method and apparatus [U.S. Pat. No. 4,484,582]; an anti-siphoning valve [U.S. Pat. No. 5,634,894]; a method of screening for silicone-specific hypersensitivity [U.S. Pat. No. 5,747,270]; and a catheter advancing single-handed soft passer [U.S. Pat. No. 6,197,003].
Shunt malfunction usually demands elective, and often urgent, open surgical intervention to revise the shunt system and restore functional integrity before permanent brain injury occurs. Such revisions require general anesthesia in addition to the operative procedure and are followed typically by a minimum hospitalization of 2 to 3 days.
Once shunt function is restored, malfunction is most likely to recur in the next few weeks or months. Subsequent malfunctions and, necessarily, further surgical revisions are unfortunately not uncommon; and these carry significant risks of shunt infection, hemorrhage or bleeding difficulties, and seizures in addition to the emotional and chological trauma endured by patients and families [see for example: Ivan, L. P. and S. H. Choo, Can. J. Sure. 23: 566-568 (1980); Keuchner, T. R. and J. Mealey, J. Neurosurg. 50: 179-186 (1979); Shurin, S. and H. L. Rekate, J. Neurosurg. 54: 264-267 (1981)]. Revision of ventriculoperitoneal shunts is also the most common performed single neurosurigcal operation in the pediatric population. Pediatric ventriculoperitoneal shunts often occlude because the choroid plexus flows into the intake drainage holes in the ventricular catheter and then becomes adherent. This results in a proximal shunt malfunction requiring surgical revision. A significant complication of this revision surgery is that removal of the catheter can avulse the choroid plexus, causing intraventricular hemorrhage; and this can be dangerous by itself or cause a high risk of occlusion of the new shunt with debris or blood.
Another frequent neurosurgical maneuver for removing shunt occlusions has been the use of a monopolar cautery. In typical usuage, a stilette is passed down the existing implanted catheter; and then the occluding tissue is coagulated with monopolar cautery to shrink the occlusion (typically the choroid plexus) and release the adhesion. This can be successful, but often can be complicated by concomitant damage to intracranial structures. Typically blood vessel damage and severe subarachnoid hemorrhages have been reported as a result of the monopolar coagulation technique. Nevertheless, monopolar cauterization continues to remain the conventionally accepted procedure and standard of care, despite the long-recognized dangerous and uncontrolled distribution of electric current and heat within the tissue which accompanies its use.
The medical dangers and substantive disadvantages of monopolar cauterization are perhaps best evidenced and exemplified by a brief, but revealing, patient case historyxe2x80x94as reported by the authors, Drs. F. A. Boop and B. C. Cherny, at the 24th Annual Meeting of the American Society of Pediatric Neurosurgeons held Jan. 28-Feb. 2, 2001. Their published Abstract and patient case history is reproduced in full below.
xe2x80x9cThe authors present the case of an 8 year old child with congenital hydrocephalus, shunted in infancy, who presented with a proximal VP shunt malfunction. At the time of surgery, the ventricular catheter was stuck to the choroid plexus. The catheter was styletted and the choroid plexus coagulated with the monopolar bovic set on 30. The catheter was replaced uneventfully and the child sent home the next day doing well. He returned to the emergency room 2 weeks later with a spontaneous frontal lobe and intraventricular hemorrhage. At that time he was found to have a 1 cm pseudo-aneurysm arising from the anterior cerebral artery. In retrospect, the tip of the ventricular catheter extended to the level of the inter-hemispheric fissure. The authors believe that thermal injury from coagulation of the catheter caused the pseudo-aneurysm, which was subsequently treated endovascularly.
The authors suggest that, in cases in which ventricular catheter is in close proximity to major cerebral vessels, extreme caution be used in manipulating the catheter and that the current of the coagulating unit be turned down low prior to coagulating the anchoring tissues.xe2x80x9d
Accordingly, even though monopolar cauterization remains the current standard of care and therapeutic technique, it is clearly evident that an improved technology which is able to provide a better distribution of electric current and heat within the adherent tissue is both desirable and needed. Were a device to be developed which offers these desirable features and advantages and also allows for an easy utilization of the coagulation cauterization technique to remove adherent cranial tissue in-situ within a previously implanted ventricular shunt, such an innovation would be recognized and accepted by practitioners as offering major benefits and advantages as well as being a marked improvement in the relevant technical field.
The present invention provides a bipolar coagulator for in-vivo coagulation cauterization of tissue which is occluding at least one sidewall hole leading to the internal lumen of a catheter previously implanted into the body of a living subject for in-vivo flow release of fluids, said bipolar coagulator comprising:
a flexible obturator of fixed dimensions and substantially cylindrical form which is configured to fit within and pass through the inner diameter of the internal lumen of the catheter previously implanted in-vivo, said flexible obturator
(i) comprising a shaped proximal end section adapted for passage within the inner diameter of the internal lumen of the implanted ventricular catheter, a distal end section, and a flexible body section adapted for passage through and around such internal lumen bends as may exist within the implanted catheter, and
(ii) being constituted at least in part of an electrically insulating material;
at least two electrodes spatially disposed at different, direction-oriented, pre-chosen positions on said exterior surface of said proximal end section of said flexible obturator, each of said electrodes comprising a discrete electrode tip disposed on said exterior proximal end surface of said obturator at a pre-chosen position and an electrically communicating electrode body which is joined to said electrode tip and which extends into the interior of said obturator, said at least two direction-oriented disposed electrodes providing at least one positively charged electrode pole and at least one negatively charged electrode pole which collectively identify
(a) a demarcated surface area between said disposed electrode poles on said exterior surface of said obturator,
(b) a discrete gapped space which exists adjacent to and over said demarcated surface area between said disposed electrode poles as a cauterization zone, and
(c) an on-demand electrode system for generating a direction-oriented and spatially-controlled flow of electrical arc current for coagulation cauterization over said gapped space of said obturator; and
electrical current conveyance apparatus which is contained internally at least within said proximal end section of said obturator and is joined to each electrode spatially disposed on said surface of said obturator.